World's most polluted cities

Severe pollution is once again choking Shanghai and other cities in China, disrupting hundreds of flights and forcing schools to close. China is home to some of the world's most polluted cities -- take a look at some of the others.

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Chernobyl, Ukraine -- Even nearly 27 years after the nuclear reactor meltdown, a 19-mile area surrounding Chernobyl remains dangerously radioactive and uninhabitable. Between 1992 and 2002, more than 4,000 cases of thyroid cancer cases were diagnosed among Russian, Ukrainian and Belarusian children living in the fallout zone, according to Time.